Fluid supply mechanism

ABSTRACT

An improved form of ink supply to ink ejection chambers is included on an ink jet print head for printing images. The supply is fabricated on a planar wafer, the supply being through wafer channels, wherein the through wafer channels each supply a plurality of fluid chambers. The through wafer channels can include etchant holes in one wall exposed to atmospheric conditions and the fluid chambers can each include a fluid filter in one wall.

CROSS REFERENCES TO RELATED APPLICATIONS

The following Australian provisional patent applications are hereby incorporated by cross-reference. For the purposes of location and identification, U.S. patent applications identified by their U.S. patent application Ser. Nos. (U.S. Ser. No.) are listed alongside the Australian applications from which the U.S. patent applications claim the right of priority.

CROSS-REFERENCED US PATENT AUSTRALIAN APPLICATION (CLAIMING PROVISIONAL RIGHT OF PRIORITY PATENT FROM AUSTRALIAN DOCKET NO. PROVISIONAL APPLICATION) NO. PO7991 09/113,060 ART01 PO8505 09/113,070 ART02 PO7988 09/113,073 ART03 PO9395 09/112,748 ART04 PO8017 09/112,747 ART06 PO8014 09/112,776 ART07 PO8025 09/112,750 ART08 PO8032 09/112,746 ART09 PO7999 09/112,743 ART10 PO7998 09/112,742 ART11 PO8031 09/112,741 ART12 PO8030 09/112,740 ART13 PO7997 09/112,739 ART15 PO7979 09/113,053 ART16 PO8015 09/112,738 ART17 PO7978 09/113,067 ART18 PO7982 09/113,063 ART19 PO7989 09/113,069 ART20 PO8019 09/112,744 ART21 PO7980 09/113,058 ART22 PO8018 09/112,777 ART24 PO7938 09/113,224 ART25 PO8016 09/112,804 ART26 PO8024 09/112,805 ART27 PO7940 09/113,072 ART28 PO7939 09/112,785 ART29 PO8501 09/112,797 ART30 PO8500 09/112,796 ART31 PO7987 09/113,071 ART32 PO8022 09/112,824 ART33 PO8497 09/113,090 ART34 PO8020 09/112,823 ART38 PO8023 09/113,222 ART39 PO8504 09/112,786 ART42 PO8000 09/113,051 ART43 PO7977 09/112,782 ART44 PO7934 09/113,056 ART45 PO7990 09/113,059 ART46 PO8499 09/113,091 ART47 PO8502 09/112,753 ART48 PO7981 09/113,055 ART50 PO7986 09/113,057 ART51 PO7983 09/113,054 ART52 PO8026 09/112,752 ART53 PO8027 09/112,759 ART54 PO8028 09/112,757 ART56 PO9394 09/112,758 ART57 PO9396 09/113,107 ART58 PO9397 09/112,829 ART59 PO9398 09/112,792 ART60 PO9399 09/112,791 ART61 PO9400 09/112,790 ART62 PO9401 09/112,789 ART63 PO9402 09/112,788 ART64 PO9403 09/112,795 ART65 PO9405 09/112,749 ART66 PO0959 09/112,784 ART68 PP1397 09/112,783 ART69 PP2370 09/112,781 DOT01 PP2371 09/113,052 DOT02 PO8003 09/112,834 Fluid01 PO8005 09/113,103 Fluid02 PO9404 09/113,101 Fluid03 PO8066 09/112,751 IJ01 PO8072 09/112,787 IJ02 PO8040 09/112,802 IJ03 PO8071 09/112,803 IJ04 PO8047 09/113,097 IJ05 PO8035 09/113,099 IJ06 PO8044 09/113,084 IJ07 PO8063 09/113,066 IJ08 PO8057 09/112,778 IJ09 PO8056 09/112,779 IJ10 PO8069 09/113,077 IJ11 PO8049 09/113,061 IJ12 PO8036 09/112,818 IJ13 PO8048 09/112,816 IJ14 PO8070 09/112,772 IJ15 PO8067 09/112,819 IJ16 PO8001 09/112,815 IJ17 PO8038 09/113,096 IJ18 PO8033 09/113,068 IJ19 PO8002 09/113,095 IJ20 PO8068 09/112,808 IJ21 PO8062 09/112,809 IJ22 PO8034 09/112,780 IJ23 PO8039 09/113,083 IJ24 PO8041 09/113,121 IJ25 PO8004 09/113,122 IJ26 PO8037 09/112,793 IJ27 PO8043 09/112,794 IJ28 PO8042 09/113,128 IJ29 PO8064 09/113,127 IJ30 PO9389 09/112,756 IJ31 PO9391 09/112,755 IJ32 PP0888 09/112,754 IJ33 PP0891 09/112,811 IJ34 PP0890 09/112,812 IJ35 PP0873 09/112,813 IJ36 PP0993 09/112,814 IJ37 PP0890 09/112,764 IJ38 PP1398 09/112,765 IJ39 PP2592 09/112,767 IJ40 PP2593 09/112,768 IJ41 PP3991 09/112,807 IJ42 PP3987 09/112,806 IJ43 PP3985 09/112,820 IJ44 PP3983 09/112,821 IJ45 PO7935 09/112,822 IJM01 PO7936 09/112,825 IJM02 PO7937 09/112,826 IJM03 PO8061 09/112,827 IJM04 PO8054 09/112,828 IJM05 PO8065 09/113,111 IJM06 PO8055 09/113,108 IJM07 PO8053 09/113,109 IJM08 PO8078 09/113,123 IJM09 PO7933 09/113,114 IJM10 PO7950 09/113,115 IJM11 PO7949 09/113,129 IJM12 PO8060 09/113,124 IJM13 PO8059 09/113,125 IJM14 PO8073 09/113,126 IJM15 PO8076 09/113,119 IJM16 PO8075 09/113,120 IJM17 PO8079 09/113,221 IJM18 PO8050 09/113,116 IJM19 PO8052 09/113,118 IJM20 PO7948 09/113,117 IJM21 PO7951 09/113,113 IJM22 PO8074 09/113,130 IJM23 PO7941 09/113,110 IJM24 PO8077 09/113,112 IJM25 PO8058 09/113,087 IJM26 PO8051 09/113,074 IJM27 PO8045 09/113,089 IJM28 PO7952 09/113,088 IJM29 PO8046 09/112,771 IJM30 PO9390 09/112,769 IJM31 PO9392 09/112,770 IJM32 PP0889 09/112,798 IJM35 PP0887 09/112,801 IJM36 PP0882 09/112,800 IJM37 PP0874 09/112,799 IJM38 PP1396 09/113,098 IJM39 PP3989 09/112,833 IJM40 PP2591 09/112,832 IJM41 PP3990 09/112,831 IJM42 PP3986 09/112,830 IJM43 PP3984 09/112,836 IJM44 PP3982 09/112,835 IJM45 PP0895 09/113,102 IR01 PP0870 09/113,106 IR02 PP0869 09/113,105 IR04 PP0887 09/113,104 IR05 PP0885 09/112,810 IR06 PP0884 09/112,766 IR10 PP0886 09/113,085 IR12 PP0871 09/113,086 IR13 PP0876 09/113,094 IR14 PP0877 09/112,760 IR16 PP0878 09/112,773 IR17 PP0879 09/112,774 IR18 PP0883 09/112,775 IR19 PP0880 09/112,745 IR20 PP0881 09/113,092 IR21 PO8006 09/113,100 MEMS02 PO8007 09/113,093 MEMS03 PO8008 09/113,062 MEMS04 PO8010 09/113,064 MEMS05 PO8011 09/113,082 MEMS06 PO7947 09/113,081 MEMS07 PO7944 09/113,080 MEMS09 PO7946 09/113,079 MEMS10 PO9393 09/113,065 MEMS11 PP0875 09/113,078 MEMS12 PP0894 09/113,075 MEMS13

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates to the supply of fluid, such as inks or the like to a mechanism such as an assay of printhead nozzles which consumes the ink supplied.

BACKGROUND OF THE INVENTION

Recently, small compact printheads have been proposed for pagewidth printheads with the printheads operating at high speeds and, in a pagewidth manner, for the printing out of ink. A printhead able to print full color pictures relies upon the supply of at least three inks (cyan, magenta and yellow) and, when operated in a pagewidth manner, is likely to consume a substantial amount of ink.

Recently, a pagewidth print-head has been proposed having full color output capabilities. A problem in providing a full color slim pagewidth inkjet printhead is the supply of ink to the printhead nozzles. Obviously, a number of different colored inks have to be supplied to ink ejection chambers within an ink jet printhead in a continuous, efficient manner so as to support high speed operation.

Preferably, any ink supply to the ejection chambers can be constructed as part of the micro-electro mechanical systems (MEMS) production process.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved form of ink supply to ink ejection chambers included on an ink jet printhead for printing images.

In accordance with a first aspect of the present invention, there is provided a fluid supply means for supplying a plurality of different fluids to a plurality of different supply slots, wherein the supply slots are being spaced apart at periodic intervals in an interleaved manner, the fluid supply means comprising a fluid inlet means for each of the plurality of different fluids, a main channel flow means for each of the different fluids, connected to said fluid inlet means and running past each of the supply slots, and sub-channel flow means connecting each of the supply slots to a corresponding main channel flow means. The number of fluids is greater than 2 and at least two of the main channel flow means run along the first surface of a molded flow supply unit and another of the main channel flow means runs along the top surface of the molded piece with the subchannel flow means being interconnected with the slots by means of through-holes through the surface of the molded piece.

Preferably, the supply means is plastic injection molded and the pitch rate of the slots is substantially less than, or equal to 1,000 slots per inch. Further the collection of slots runs substantially the width of a photograph. Preferably, the fluid supply means further comprises a plurality of roller slot means for the reception of one or more pinch rollers and the fluid comprises ink and the rollers are utilised to control the passage of a print media across the printhead interconnected to the slots. The slots are divided into corresponding color slots with each series of color slots being arranged in columns.

Preferably, at least one of the channels of the fluid supply means is exposed when fabricated and is sealed by means of utilising sealing tape to seal the exposed surface of the channel. Advantageously, the fluid supply means is further provided with a TAB slot for the reception of tape automated bonded (TAB) wires.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drafts in which:

FIG. 1 illustrates an exploded perspective view in section of a printing system an ink jet printhead and an ink supply unit in accordance with the invention incorporating;

FIG. 2 illustrates a perspective view, partly in section, of the ink supply unit of FIG. 1;

FIG. 3 illustrates a bottom perspective view, partly in section, of the ink supply unit of FIG. 1;

FIG. 4 illustrates an enlarged top view of the ink supply unit of FIG. 1;

FIG. 5 illustrates an enlarged bottom view, partly in section, of the ink supply unit of FIG. 1;

FIGS. 6 and 7 illustrate a perspective view of the ink supply unit showing placement of rollers therein; and

FIG. 8 illustrates schematically a side perspective partly in section of the printhead of FIG. 1.

DESCRIPTION OF THE PREFERRED AND OTHER EMBODIMENTS

In the preferred embodiment, there is provided an fluid or ink supply unit for the supply of ink to a pagewidth printhead the width of the page being variable in accordance with requirements.

Turning initially to FIG. 1, there is illustrated an exploded perspective view, in section, of a full printing system 1 based around a printhead 2 which ejects ink drops on demand on to print media 3 so as to form an image. The print media 3 is pinched between two sets of rollers comprising a first set 5, 6 and second set 7, 8. The printhead 2 is constructed in accordance with the principles as outlined in specifications relating to ink jets as set out above under the heading Cross References to Related Applications.

The print head 2 operates under the control of power, ground and signal lines 10 which provide power and control for the printhead 2 and are bonded by means of Tape Automated Bonding (TAB) to the surface of the printhead 2.

Importantly, the printhead 2, which can be constructed from a silicon wafer device suitably separated, relies upon a series of anisotropic etches 12 through the wafer. The through wafer etches form through wafer channels 12 to allow for the direct supply of ink to the printhead surface from the back of the wafer for subsequent ejection.

The ink is supplied to the back of the printhead 2 by means of an ink supply unit 14 in accordance with the invention. The printhead 2 has three separate rows along its surface for the supply of separate colors of ink. The ink supply unit 14 also includes a lid 15 for the sealing of ink channels.

In FIGS. 2-7, there are illustrated various perspective views of the ink supply unit 14. Each of FIGS. 2-7 illustrate only a portion of the supply unit 14 which can be constructed of indefinite length, the portions only shown to provide exemplary details. In FIG. 2, there is illustrated a bottom perspective view, FIG. 3 illustrates a top perspective view, FIG. 4 illustrates a close up bottom perspective view, partly in sections, FIG. 5 illustrates a top side perspective view showing details of the ink channels, and FIG. 6 illustrates a top side perspective view as does FIG. 7.

There is considerable cost advantage in forming ink supply unit 14 from injection molded plastic instead of, say, micromachined silicon. The manufacturing cost of a plastic ink channel will be considerably less in volume and manufacturing is substantially easier. The design illustrated in the accompanying drawings assumes a 1600 dpi three color monolithic print head, of a predetermined length. The provided flow rate calculations are for a 100 mm photo printer.

The ink supply unit 14 contains all of the required fine details. The lid 15 (FIG. 1) is permanently glued or ultrasonically welded to the ink supply unit 14 and provides a seal for the ink channels.

Turning to FIG. 2, the cyan, magenta and yellow ink flows in through ink inlets 20-22, the magenta ink flows through holes 24, 25 and along magenta main channels 26, 27 (FIG. 3). The cyan ink flows along cyan main channel 30 and the yellow ink flows along the yellow main channel 31. As best seen in FIG. 4, the cyan ink in the cyan main channel 30 then flows into a cyan subchannel 33. The yellow subchannel 34 similarly receives yellow ink from the yellow main channel 31.

As best seen in FIG. 5, the magenta ink also flows from magenta main channels 26, 27 through magenta holes 36, 37. Returning again to FIG. 4, the magenta ink flows out of the holes 36, 37. The magenta ink flows along a first magenta subchannel 38 and then along second magenta subchannel 39 before flowing into a magenta pit area 40. The magenta ink then flows through magenta vias e.g. 42 which are aligned with corresponding through wafer channels 12 wherein they subsequently supply ink to inkjet nozzles for ejection.

Similarly, the cyan ink within the cyan subchannel 33 flows into a cyan pit area 45 which supplied ink to cyan vias 43, 44. Similarly, the yellow subchannel 34 supplies yellow pit area 46 which in turn supplies yellow vias 47, 48.

As seen in FIG. 5, the printhead 2 is designed to be received within a printhead slot 50 defined by the ink supply unit 14 with the various vias e.g. 51 aligned with corresponding through wafer channels, e.g. 12 in the printhead wafer (FIG. 1).

Returning to FIG. 1, care must be taken to provide adequate ink flow to the entire printhead 2, while satisfying the constraints of an injection molding process. The size of the ink through wafer channels 12 at the back of the printhead 2 is approximately 100 μm×50 μm, and the spacing between through wafer channels 12 carrying different colors of ink is approximately 170 μm. While features of this size can readily be molded in plastic (compact discs have micron sized features), in general to allow release of injection molded components, the height of the wall should not exceed the thickness of the wall by a large factor. The preferred embodiment overcomes these problems by using a hierarchy of progressively smaller ink channels.

In FIG. 8, there is illustrated schematically, a section of an array 70 of printhead 2 of FIG. 1. The array 70 is formed on the front surface 84 of a single planar wafer by known chip manufacturing techniques such as anisotropic etching as referred to above. The wafer extends downwardly (as seen in FIG. 8) from the front surface 84 to a back surface shown at 85 in FIG. 1. The section is divided into 3 series of nozzles comprising the cyan series 71, the magenta series 72 and the yellow series 73. Each series of nozzles is further divided into two rows, 75, 76 with the print-head 70 having a series of bond pads 78 for bonding of power in control signals. On a top surface of each through wafer channel 12 there is preferably provided a series of etching apertures 79 interconnecting with the ambient atmosphere and which can be utilized in etching the through wafer channels 81 and are dimensioned so that surface tension restricts the flow of fluid through apertures 79 during operation.

The printhead 2 includes the ink supply channels in the form of through wafer channels 81, equivalent to through wafer channel 12 of FIG. 1. The ink flows from the back of the wafer through the channels 81 into supply conduits 80 which run parallel to, and just beneath, the front surface 84, and in turn through filter grills 82 formed by spaced apart struts, to nozzle chambers, 83. The operation of the nozzle chambers 83 and printhead 2 (FIG. 1) is, as mentioned previously, as described in the disclosures of the cross-referenced applications mentioned above.

Ink Channel Fluid Flow Analysis

Turning now to an analysis of the ink flow, the main ink channels 26, 27, 30, 31 (FIG. 2, FIG. 3) are around 1 mm×1 mm, and supply all of the nozzles of one color. The subchannels 33, 34, 38, 39 (FIG. 4) are around 200 μm×100 μm and supply about 25 inkjet nozzles each. The vias 43, 44, 47, 48 and through wafer channels 81 (FIG. 6) are 100 μm×50 μm and supply 3 nozzles at each side of the printhead through wafer channels. Each filter grill 82 has 8 slits, each with an area of 20 μm×2 μm and supplies a single nozzle.

An analysis has been conducted of the pressure requirements of an ink jet printer constructed as described. The analysis is for a 1,600 dpi three color process print head for photograph printing. The print width was 100 mm which gives 6,250 nozzles for each color, giving a total of 18,750 nozzles.

The maximum ink flow rate required in various channels for full black printing is important. It determines the pressure drop along the ink channels, and therefore whether the print head will stay filled by the surface tension forces alone, or, if not, the ink pressure that is required to keep the print head full.

To calculate the pressure drop, a drop volume of 2.5 pl for 1,600 dpi operation was utilized. While the nozzles may be capable of operating at a higher rate, the chosen drop repetition rate is 5 KHz which is suitable to print a 150 mm long photograph in an little under 2 seconds. Thus, the print head, in the extreme case, has a 18,750 nozzles, all printing a maximum of 5,000 drops per second. This ink flow is distributed over the hierarchy of ink channels. Each ink channel effectively supplies a fixed number of nozzles when all nozzles are printing.

The pressure drop Ap was calculated according to the Darcy-Weisbach formula: ${\Delta \quad \rho} = \frac{\rho \quad U^{2}{fL}}{2\quad D}$

Where ρ is the density of the ink, U is the average flow velocity, L is the length, D is the hydraulic diameter, and f is a dimensionless friction factor calculated as follows: $f = \frac{k}{Re}$

Where Re is the Reynolds number and k is a dimensionless friction coefficient dependant upon the cross section of the channel, both calculated as follows: ${Re} = \frac{UD}{v}$

Where ν is the kinematic viscosity of the ink, and for a rectangular cross section, k can be approximated by: $k = {\frac{64}{\frac{2}{3} + \frac{11b}{24\quad a}}\left\lbrack {\frac{11b}{24a}\left( {2 - \frac{b}{a}} \right)} \right\rbrack}$

Where a is the longest side of the rectangular cross section, and b is the shortest side. The hydraulic diameter D for a rectangular cross section is given by: $D = \frac{2{ab}}{a + b}$

Ink is drawn off the main ink channels at 250 points along the length of the channels. The ink velocity falls linearly from the start of the channel to zero at the end of the channel, so the average flow velocity U is half of the maximum flow velocity. Therefore, the pressure drop along the main ink channels is half of that calculated using the maximum flow velocity.

Utilizing these formulas, the pressure drops can be calculated in accordance with the following tables:

Table of Ink Channel Dimensions and Pressure Drops Number of Nozzles Max. ink flow Pressure Items Length Width Depth supplied at 5 KHz(U) drop Δρ Central Moulding   1 106 mm 6.4 mm 1.4 mm 18,750 0,23 ml/seC NA Cyan main channel (30)   1 100 mm 1 mm 1 mm 6,250 0.16 μl/μs 111 Pa Magenta main channel (26)   2 100 mm 700 μm 700 μm 3,125 0.16 μl/μs 231 Pa Yellow main channel (31)   1 100 mm 1 mm 1 mm 6,250 0.16 μl/μs 111 Pa Cyan sub-channel (33)  250 1.5 mm 200 μm 100 μm 25 0.16 μl/μs 41.7 Pa Magenta sub-channel (34)(a)  500 200 μm 50 μm 100 μm 12.5 0,031 μl/μs 44.5 Pa Magenta sub-channel (38)(b)  500 400 μm 100 μm 200 μm 12.5 0.031 μl/μs 5.6 Pa Yellow sub-channel (34)  250 1.5 mm 200 μm 100 μm 25 0.016 μl/μs 41.7 Pa Cyan pit (42)  250 200 μm 100 μm 300 μm 25 0.010 μl/μs 3.2 Pa Magenta through (40)  500 200 μm 50 μm 200 μm 12.5 0.016 μl/μs 18.0 Pa Yellow pit (46)  250 200 μm 100 μm 300 μm 25 0.010 μl/μs 3.2 Pa Cyan via (43)  500 100 μm 50 μm 100 μm 12.5 0.031 μl/μs 22.3 Pa Magenta via (42)  500 100 μm 50 μm 100 μm 12.5 0.031 μl/μs 22.3 Pa Yellow via  500 100 μm 50 μm 100 μm 12.5 0.031 μl/μs 22.3 Pa Magenta through hole (37)  500 200 μm 500 μm 100 μm 12.5 0.0031 μl/μs 0.87 Pa Chip slot   1 100 mm 730 μm 625 18,750 NA NA Print head through holes 1500 600μ 100 μm 50 μm 12.5 0.052 μl/μs 133 Pa (81)(in the chip substrate) Print head channel segments 1,000/  50 μm 60 μm 20 μm 3.125 0.049 μl/μs 62.8 Pa (on chip front) color Filter Slits (on entrance to 8 per 2 μm 2 μm 20 μm 0.125 0.039 μl/μs 251 Pa nozzle chamber (82) nozzle Nozzle chamber (on chip 1 per 70 μm 30 μm 20 μm 1 0.021 μl/μs 75.4 Pa front)(83) nozzle

The total pressure drop from the ink inlet to the nozzle is therefore approximately 701 Pa for cyan and yellow, and 845 Pa for magenta. This is less than 1% of atmospheric pressure. Of course, when the image printed is less than full black, the ink flow (and therefore the pressure drop) is reduced from these values.

Making the Mold for the Ink-head Supply Unit The ink head supply unit 14 (FIG. 1) has features as small as 50 μ and a length of 106 mm. It is impractical to machine the injection molding tools in the conventional manner. However, even though the overall shape may be complex, there are no complex curves required. The injection molding tools can be made using conventional milling for the main ink channels and other millimeter scale features, with a lithographically fabricated inset for the fine features. A LIGA process can be used for the inset.

A single injection molding tool could readily have 50 or more cavities, so could make many millions of ink channels per year, at a minimal cost. Most of the tool complexity is in the inset. As the insets are replicated lithographically, the total toolmaking cost should not be excessive.

Returning to FIG. 1, the printing system 1 is constructed via the molding ink supply unit 14 and the lid 15 together and sealing them together as previously described. Subsequently the printhead 2 is placed in its corresponding slot 50. Adhesive sealing strips 52, 53 are placed over the magenta main channels so to ensure they are properly sealed. The Tape Automated Bonding (TAB) strip 10 is then connected to the printhead 2 with the tab bonding wires running in the cavity 55. As can best be seen from FIGS. 6 and 7, aperture slots are 55-62 are provided for the snap in insertion of rollers 5, 7 (FIG. 1). The slots provided for the “clipping in” of rollers with a small degree of play subsequently being provided for simple rotation of the rollers.

It would be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiment without departing from the spirit or scope of the invention as broadly described. The present embodiment is, therefore, to be considered in all respects to be illustrative and not restrictive.

Ink Jet Technologies

The embodiments of the invention use an ink jet printer type device. Of course many different devices could be used. However presently popular ink jet printing technologies are unlikely to be suitable.

The most significant problem with thermal inkjet is power consumption. This is approximately 100 times that required for high speed, and stems from the energy-inefficient means of drop ejection. This involves the rapid boiling of water to produce a vapor bubble which expels the ink. Water has a very high heat capacity, and must be superheated in thermal inkjet applications. This leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.

The most significant problem with piezoelectric inkjet is size and cost. Piezoelectric crystals have a very small deflection at reasonable drive voltages, and therefore require a large area for each nozzle. Also, each piezoelectric actuator must be connected to its drive circuit on a separate substrate. This is not a significant problem at the current limit of around 300 nozzles per print head, but is a major impediment to the fabrication of pagewidth print heads with 19,200 nozzles.

Ideally, the inkjet technologies used meet the stringent requirements of in-camera digital color printing and other high quality, high speed, low cost printing applications. To meet the requirements of digital photography, new inkjet technologies have been created. The target features include:

low power (less than 10 Watts)

high resolution capability (1,600 dpi or more)

photographic quality output

low manufacturing cost

small size (pagewidth times minimum cross section)

high speed (<2 seconds per page).

All of these features can be met or exceeded by the inkjet systems described below with differing levels of difficulty. Forty-five different inkjet technologies have been developed by the Assignee to give a wide range of choices for high volume manufacture. These technologies form part of separate applications assigned to the present Assignee as set out in the table under the heading Cross References to related applications.

The inkjet designs shown here are suitable for a wide range of digital printing systems, from battery powered one-time use digital cameras, through to desktop and network printers, and through to commercial printing systems For ease of manufacture using standard process equipment, the printhead is designed to be a monolithic 0.5 micron CMOS chip with MEMS post processing. For color photographic applications, the printhead is 100 mm long, with a width which depends upon the inkjet type. The smallest printhead designed is IJ38, which is 0.35 mm wide, giving a chip area of 35 square mm. The printheads each contain 19,200 nozzles plus data and control circuitry.

Ink is supplied to the back of the printhead by injection molded plastic ink channels. The molding requires 50 micron features, which can be created using a lithographically micromachined insert in a standard injection molding tool. Ink flows through holes etched through the wafer to the nozzle chambers fabricated on the front surface of the wafer. The printhead is connected to the camera circuitry by tape automated bonding.

Tables of Drop-on-Demand Ink Jets

The present invention is useful in the field of digital printing, in particular, ink jet printing. A number of patent applications in this field were filed simultaneously and incorporated by cross reference.

Eleven important characteristics of the fundamental operation of individual ink jet nozzles have been identified. These characteristics are largely orthogonal, and so can be elucidated as an eleven dimensional matrix. Most of the eleven axes of this matrix include entries developed by the present assignee.

The following tables form the axes of an eleven dimensional table of ink jet types.

Actuator mechanism (18 types)

Basic operation mode (7 types)

Auxiliary mechanism (8 types)

Actuator amplification or modification method (17 types)

Actuator motion (19 types)

Nozzle refill method (4 types)

Method of restricting back-flow through inlet (10 types)

Nozzle clearing method (9 types)

Nozzle plate construction (9 types)

Drop ejection direction (5 types)

Ink type (7 types)

The complete eleven dimensional table represented by these axes contains 36.9 billion possible configurations of ink jet nozzle. While not all of the possible combinations result in a viable ink jet technology, many million configurations are viable. It is clearly impractical to elucidate all of the possible configurations. Instead, certain ink jet types have been investigated in detail. These are designated IJ01 to IJ45 which matches the docket numbers in the in the table under the heading Cross References to Related Applications.

Other ink jet configurations can readily be derived from these forty-five examples by substituting alternative configurations along one or more of the 11 axes. Most of the IJ01 to IJ45 examples can be made into ink jet printheads with characteristics superior to any currently available ink jet technology.

Where there are prior art examples known to the inventor, one or more of these examples are listed in the examples column of the tables below. The IJ01 to IJ45 series are also listed in the examples column. In some cases, a print technology may be listed more than once in a table, where it shares characteristics with more than one entry.

Suitable applications for the ink jet technologies include: Home printers, Office network printers, Short run digital printers, Commercial print systems, Fabric printers, Pocket printers, Internet WWW printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.

The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.

Description Advantages Disadvantages Examples ACTUATOR MECHANISM (APPLIED ONLY TO SELECTED INK DROPS) Thermal bubble An electrothermal heater heats Large force generated High power Canon Bubblejet 1979 Endo et the ink to above boiling point, Simple construction Ink carrier limited to water al GB patent 2,007,162 transferring significant heat to No moving parts Low efficiency Xerox heater-in-pit 1990 the aqueous ink. A bubble Fast operation High temperatures required Hawkins et al U.S. Pat. No. nucleates and quickly forms, Small chip area required for High mechanical stress 4,899,181 expelling the ink. The efficiency actuator Unusual materials required Hewlett-Packard TIJ 1982 of the process is low, with Large drive transistors Vaught et al U.S. Pat. No. typically less than 0.05% of the Cavitation causes actuator 4,490,728 electrical energy being trans- failure formed into kinetic energy of the Kogation reduces bubble drop. formation Large print heads are difficult to fabricate Piezoelectric A piezoelectric crystal such as Low power consumption Very large area required for Kyser et al U.S. Pat. No. lead lanthanum zirconate (PZT) Many ink types can be used actuator 3,946,398 is electrically activated, and Fast operation Difficult to integrate with Zoltan U.S. Pat. No. 3,683,212 either expands, shears, or bends High efficiency electronics 1973 Stemme U.S. Pat. No. to apply pressure to the ink, High voltage drive transistors 3,747,120 ejecting drops. required Epson Stylus Full pagewidth print heads Tektronix impractical due to actuator size IJ04 Requires electrical poling in high field strengths during manufacture Electrostrictive An electric field is used to Low power consumption Low maximum strain (approx. activate electrostriction in Many ink types can be used 0.01%) relaxor materials such as lead Low thermal expansion Large area required for actuator Seiko Epson, Usui et all JP lanthanum zirconate titanate Electric field strength required due to low strain 253401/96 (PLZT) or lead magnesium (approx. 3.5 V/μm) can be Response speed is marginal IJ04 niobate (PMN). generated without difficulty (˜10 μs) Does not require electrical High voltage drive transistors poling required Full pagewidth print heads impractical due to actuator size Ferroelectric An electric field is used to Low power consumption Difficult to integrate with IJ04 induce a phase transistion Many ink types can be used electronics between the antiferroelectric Fast operation (<1 μs) Unusual materials such as (AFE) and ferroelectric (FE) Relatively high longitudinal PLZSnT are required phase. Perovskite materials such strain Actuators require a large area as tin modified lead lanthanum High efficiency zirconate titanate (PLZSnT) Electric field strength of around exhibit large strains of up to 1% 3 V/μm can be readily provided associated with the AFE to FE phase transition. Electrostatic Conductive plates are separated Low power consumption Difficult to operate electrostatic IJ02, IJ04 plates by a compressible or fluid Many ink types can be used devices in an aqueous environ- dielectric (usually air). Upon Fast operation ment application of a voltage, the The electrostatic actuator will plates attract each other and normally need to be separated displace ink, causing drop from the ink ejection. The conductive plates Very large area required to may be in a comb or honeycomb achieve high forces structure, or stacked to increase High voltage drive transistors the surface area and therefore may be required the force. Full pagewidth print heads are not competitive due to actuator size Electrostatic A strong electric field is applied Low current consumption High voltage required 1989 Saito et al, U.S. Pat. No. pull on ink to the ink, whereupon electro- Low temperature May be damaged by sparks due 4,799,068 static attraction accelerates the to air breakdown 1989 Miura et al, U.S. Pat. No. ink towards the print medium. Required field strength increases 4,810,954 as the drop size decreases Tone-jet High voltage drive transistors required Electrostatic field attracts dust Permanent An electromagnet directly Low power consumption Complex fabrication IJ07, IJ10 magnet electro- attracts a permanent magnet, Many ink types can be used Permanent magnetic material magnetic displacing ink and causing drop Fast operation such as Neodymium Iron Boron ejection. Rare earth magnets High efficiency (NdFeB) required. with a field strength around Easy extension from single High local currents required 1 Telsa can be used. Examples nozzles to pagewidth print heads Copper metalization should be are: Samarium Cobalt (SaCo) used for long electromigration and magnetic materials in the lifetime and low resistivity neodymium iron boron family Pigmented inks are usually (NdFeB, NyDyFeBNb, infeasible NdDyFeB, etc) Operating temperature limited to the Curie temperature (around 540 K.) Soft magnetic A solenoid induced a magnetic Low power consumption Complex fabrication IJ01, IJ05, IJ08, IJ10, IJ12, IJ14, core electro- field in a soft magnetic core or Many ink types can be used Materials not usually present in IJ15, IJ17 magnetic yoke fabricated from a ferrous Fast operation a CMOS fab such as NiFe, material such as electroplated High efficiency CoNiFe, or CoFe are required iron alloys such as CoNiFe [1], Easy extension from single High local currents required CoFe, or NiFe alloys. Typically, nozzles to pagewidth print heads Copper metalization should be the soft magnetic material is in used for long electromigration two parts, which are normally lifetime and low resistivity held apart by a spring. When the Electroplating is required solenoid is actuated, the two High saturation flux density is parts attract, displacing the ink. required (2.0-2.1 T is achievable with CoNiFe [1]) Lorenz force The Lorenz force acting on a Low power consumption Force acts as a twisting motion IJ06, IJ11, IJ13, IJ16 current carrying wire in a Many ink types can be used Typically, only a quarter of the magnetic field is utilized. This Fast operation solenoid length provides force allows the magnetic field to be High efficiency in a useful direction supplied externally to the print Easy extension from single High local currents required head, for example with rare nozzles to pagewidth print heads Copper metalization should be earth permanent magnets. Only used for long electromigration the current carrying wire need be lifetime and low resistivity fabricated on the print-head, Pigmented inks are usually simplifying materials require- infeasible ments. Magneto- The actuator uses the giant Many ink types can be used Force acts as a twisting motion Fischenbeck, U.S. Pat. No. striction magnetostrictive effect of Fast operation Unusual materials such as 4,032,929 materials such as Terfenol-D Easy extension from single Terfenol-D are required IJ25 an alloy of terbium, dysporsium nozzles to pagewidth print heads High local currents required and iron developed at the Naval High force is available Copper metalization should be Ordnance Laboratory, hence used for long electromigration Ter-Fe-NOL). For best lifetime and low resistivity efficiency, the actuator should Pre-stressing may be required be pre-stressed to approx. 8 MPa. Surface tension Ink under positive pressure is Low power consumption Requires supplementary force to Silverbrook, EP 0771 658 A2 reduction held in a nozzle by surface Simple construction effect drop separation and related patent applications tension. The surface tension of No unusual materials required in Requires special ink surfactants the ink is reduced below the fabrication Speed may be limited by sur- bubble threshold, causing the High efficiency factant properties ink to egress from the nozzle. Easy extension from single nozzles to pagewidth print heads Viscosity The ink viscosity is locally Simple construction Requires supplementary force to Silverbrook, EP 0771 658 A2 reduction reduced to select which drops No unusual materials required in effect drop separation and related patent applications are to be ejected. A viscosity fabrication Requires special ink viscosity reduction can be achieved Easy extension from single properties electrothermally with most inks, nozzles to pagewidth print heads High speed is difficult to achieve but special inks can be engineer- Requires oscillating ink pressure ed for a 100:1 viscosity reduc- A high temperature difference tion. (typically 80 degrees) is required Acoustic An acoustic wave is generated Can operate without a nozzle Complex drive circuitry 1993 Hadimioglu et al, EUP and focussed upon the drop plate Complex fabrication 550,192 ejection region. Low efficiency 1993 Elrod et al, EUP 572,220 Poor control of drop position Poor control of drop volume Thermoelastic An actuator which relies upon Low power consumption Efficient aqueous operation IJ03, IJ09, IJ17, IJ18, IJ19, IJ20, bend actuator differential thermal expansion Many ink types can be used requires a thermal insulator on IJ21, IJ22, IJ23, IJ24, IJ27, IJ28, upon Joule heating is used. Simple planar fabrication the hot side IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, Small chip area required for Corrosion prevention can be IJ35, IJ36, IJ37, IJ38, IJ39, IJ40, each actuator difficult IJ41 Fast operation Pigmented inks may be infeas- High efficiency ible, as pigment particles may CMOS compatible voltages and jam the bend actuator currents Standard MEMS processes can be used Easy extension from single nozzles to pagewidth print heads High CTE A material with a very high High force can be generated Requires special material (e.g. IJ09, IJ17, IJ18, IJ20, IJ21, IJ22, thermoelastic coefficient of thermal expansion Three methods of PTFE deposi- PTFE) IJ23, IJ24, IJ27, IJ28, IJ29, IJ30, actuator (CTE) such as polytetrafluoro- tion are under development: Requires a PTFE deposition pro- IJ31, IJ42, IJ43, IJ44 ethylene (PTFE) is used. As chemical vapor deposition cess, which is not yet standard in high CTE materials are usually (CVD), spin coating, and ULSI fabs non-conductive, a heater fabri- evaporation PTFE deposition cannot be cated from a conductive material PTFE is a candidate for low followed with high temperature is incorporated. A 50 μm long dielectric constant insulation in (above 350° C.) processing PTFE bend actuator with poly- ULSI Pigmented inks may be infeas- silicon heater and 15 mW power Very low power consumption ible, as pigment particles may input can provide 180 μN force Many ink types can be used jam the bend actuator and 10 μm deflection. Actuator Simple planar fabrication motions include: Small chip area required for Bend each actuator Push Fast operation Buckle High efficiency Rotate CMOS compatible voltages and currents Easy extension from single nozzles to pagewidth print heads Conductive A polymer with a high co- High force can be generated Requires special materials IJ24 polymer efficient of thermal expansion Very low power consumption development (High CTE con- thermoelastic (such as PTFE) is doped with Many ink types can be used ductive polymer) actuator conducting substances to Simple planar fabrication Requires a PTFE deposition increase its conductivity to Small chip area required for process, which is not yet about 3 order of magnitude each actuator standard in ULSI fabs below that of copper. The Fast operation PTFE deposition cannot be conducting polymer expands High efficiency followed with high temperature when resistively heated. CMOS compatible voltages and (above 350° C.) processing Examples of conducting dopants currents Evaporation and CVD deposi- include: Easy extension from single tion techniques cannot be used Carbon nanotubes nozzles to pagewidth print heads Pigmented inks may be infeas- Metal fibers ible, as pigment particles may Conductive polymers such as jam the bend actuator doped polythiophene Carbon granules Shape memory A shape memory alloy such as High force is available (stresses Fatigue limits maximum number IJ26 alloy TiNi (also known as Nitinol - of hundreds of MPa) of cycles Nickel Titanium alloy developed Large strain is available (more Low strain (1%) is required to at the Naval Ordnance Labora- than 3%) extend fatigue resistance tory) is thermally switched High corrosion resistance Cycle rate limited by heat between its weak martensitic Simple construction removal state and its high stiffness Easy extension from single Requires unusual materials austenic state. The shape of the nozzles to pagewidth print heads (TiNi) actuator in its martensitic state is Low voltage operation The latent heat of transformation deformed relative to the austenic must be provided shape. The shape change causes High current operation ejection of a drop. Requires pre-stressing to distort the martensitic state Linear Linear magnetic actuators Linear Magnetic actuators can Requires unusual semiconductor IJ12 Magnetic include the Linear Induction be constructed with high thrust, materials such as soft magnetic Actuator Actuator (LIA), Linear long travel, and high efficiency alloys (e.g. CoNiFe) Permanent Magnet Synchronous using planar semiconductor fab- Some varieties also require Actuator (LPMSA), Linear rication techniques permanent magnetic materials Reluctance Synchronous Long actuator travel is available such as Neodymium iron boron Actuator (LRSA), Linear Medium force is available (NdFeB) Switched Reluctance Actuator Low voltage operation Requires complex multi-phase (LSRA), and the Linear Stepper drive circuitry Actuator (LSA). High current operation BASIC OPERATION MODE Actuator This is the simplest mode of Simple operation Drop repetition rate is usually Thermal ink jet directly pushes operation: the actuator directly No external fields required limited to around 10 kHz. How- Piezoelectric ink jet ink supplies sufficient kinetic energy Satellite drops can be avoided if ever, this is not fundamental IJ01, IJ02, IJ03, IJ04, IJ05, IJ06, to expel the drop. The drop must drop velocity is less than 4 m/s to the method, but is related IJ07, IJ09, IJ11, IJ12, IJ14, IJ16, have a sufficient velocity to Can be efficient, depending to the refill method normally IJ20, IJ22, IJ23, IJ24, IJ25, IJ26, overcome the surface tension. upon the actuator used used IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, All of the drop kinetic energy IJ33, IJ34, IJ35, IJ36, IJ37, IJ38, must be provided by the actuator IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Satellite drops usually form if drop velocity is greater than 4.5 m/s Proximity The drops to be printed are Very simple print head fabrica- Requires close proximity Silverbrook, EP 0771 658 A2 selected by some manner (e.g. tion can be used between the print head and the and related patent applications thermally induced surface The drop selection means does print media or transfer roller tension reduction of pressurized not need to provide the energy May require two print heads ink). Selected drops are separ- required to separate the drop printing alternate rows of the ated from the ink in the nozzle from the nozzle image by contact with the print Monolithic color print heads medium or a transfer roller. are difficult Electrostatic The drops to be printed are Very simple print head fabrica- Requires very high electrostatic Silverbrook, EP 0771 658 A2 pull on ink selected by some manner (e.g. tion can be used field and related patent applications thermally induced surface The drop selection means does Electrostatic field for small tension reduction of pressurized not need to provide the energy nozzle sizes is above air break- ink). Selected drops are required to separate the drop down separated from the ink in the from the nozzle Electrostatic field may attract nozzle by a strong electric dust field. Magnetic pull The drops to be printed are Very simple print head fabrica- Requires magnetic ink Silverbrook, EP 0771 658 A2 on ink selected by some manner (e.g. can be used Ink colors other than black are and related patent applications thermally induced surface The drop selection means does difficult tension reduction of pressurized not need to provide the energy Requires very high magnetic ink). Selected drops are required to separate the drop fields separated from the ink in the from the nozzle nozzle by a strong magnetic field acting on the magnetic ink. Shutter The actuator moves a shutter to High speed (>50 kHz) operation Moving parts are required IJ13, IJ17, IJ21 block ink flow to the nozzle. can be achieved due to reduced Requires ink pressure modulator The ink pressure is pulsed at a refill time Friction and wear must be multiple of the drop ejection Drop timing can be very considered frequency. accurate Stiction is possible The actuator energy can be very low Shuttered grill The actuator moves a shutter to Actuators with small travel can Moving parts are required IJ08, IJ15, IJ18, IJ19 block ink flow through a grill to be used Requires ink pressure modulator the nozzle. The shutter move- Actuators with small force can Friction and wear must be con- ment need only be equal to the be used sidered width of the grill holes. High speed (>50 kHz) operation Stiction is possible can be achieved Pulsed mag- A pulsed magnetic field attracts Extremely low energy operation Requires an external pulsed IJ10 netic pull on an ‘ink pusher’ at the drop is possible magnetic field ink pusher ejection frequency. An actuator No heat dissipation problems Requires special materials for controls a catch, which prevents both the actuator and the ink the ink pusher from moving pusher when a drop is not to be ejected. Complex construction AUXILIARY MECHANISM (APPLIED TO ALL NOZZLES) None The actuator directly fires the Simplicity of construction Drop ejection energy must be Most ink jets, including piezo- ink drop, and there is no external Simplicity of operation supplied by individual nozzle electric and thermal bubble. field or other mechanism re- Small physical size actuator IJ01, IJ02, IJ03, IJ04, IJ05, IJ07, quired. IJ09, IJ11, IJ12, IJ14, IJ20, IJ22, IJ23, IJ24, IJ25, IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Oscillating ink The ink pressure oscillates, Oscillating ink pressure can Requires external ink pressure Silverbrook EP 0771 658 A2 pressure providing much of the drop provide a refill pulse, allowing oscillator and related patent applications (including ejection energy. The actuator higher operating speed Ink pressure phase and ampli- IJ08, IJ13, IJ15, IJ17, IJ18, IJ19, acoustic selects which drops are to be The actuators may operate with tude must be carefully controlled IJ21 stimulation) fired by selectively blocking much lower energy Acoustic reflections in the ink or enabling nozzles. The ink Acoustic lenses can be used to chamber must be designed for pressure oscillation may be focus the sound on the nozzles achieved by vibrating the print head, or preferably by an actuator in the ink supply. Media The print head is placed in close Low power Precision assembly required Silverbrook, EP 0771 658 A2 proximity proximity to the print medium. High accuracy Paper fibers may cause problems and related patent applications Selected drops protrude from the Simple print head construction Cannot print on rough substrates print head further than unsel- ected drops, and contact the print medium. The drop soaks into the medium fast enough to cause drop separation. Transfer roll Drops are printed to a transfer High accuracy Bulky Silverbrook, EP 0771 658 A2 roller instead of straight to the Wide range of print substrates Expensive and related patent applications print medium. A transfer roller can be used Complex construction Tektronix hot melt piezoelectric can also be used for proximity Ink can be dried on the transfer ink jet drop separation. roller Any of the IJ series Electrostatic An electric field is used to Low power Field strength required for Silverbrook, EP 0771 658 A2 accelerate selected drops Simple print head construction separation of small drops is near and related patent applications towards the print medium. or above air breakdown Tone-Jet Direct mag- A magnetic field is used to Low power Requires magnetic ink Silverbrook, EP 0771 658 A2 netic field accelerate selected drops of Simple print head construction Requires strong magnetic field and related patent applications magnetic ink towards the print medium. Cross magnetic The print head is placed in a Does not require magnetic Requires external magnet IJ06, IJ16 field constant magnetic field. The materials to be integrated in the Current densities may be high, Lorenz force in a current carry- print head manufacturing resulting in electromigration ing wire is used to move the process problems actuator. Pulsed mag- A pulsed magnetic field is used Very low power operation is Complex print head construction IJ10 netic field to cyclically attract a paddle, possible Magnetic materials required in which pushes on the ink. A Small print head size print head small actuator moves a catch, which selectively prevents the paddle from moving. ACTUATOR AMPLIFICATION OR MODIFICATION METHOD None No actuator mechanical amplifi- Operational simplicity Many actuator mechanisms have Thermal Bubble Ink jet cation is used. The actuator insufficient travel, or insufficient IJ01, IJ02, IJ06, IJ07, IJ16, IJ25, directly drives the drop ejection force, to efficiently drive the IJ26 process. drop ejection process Differential An actuator material expands Provides greater travel in a High stresses are involved Piezoelectric expansion bend more on one side than on the reduced print head area Care must be taken that the IJ03, IJ09, IJ17, IJ18, IJ19, IJ20, actuator other. The expansion may be materials do not delaminate IJ21, IJ22, IJ23, IJ24, IJ27, IJ29, thermal, piezoelectric, magneto- Residual bend resulting from IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, strictive, or other mechanism. high temperature or high stress IJ36, IJ37, IJ38, IJ39, IJ42, IJ43, The bend actuator converts a stress during formation IJ44 high force low travel actuator mechanism to high travel, lower force mechanism. Transient bend A trilayer bend actuator where Very good temperature stability High stresses are involved IJ40, IJ41 actuator the two outside layers are High speed, as a new drop can Care must be taken that the identical. This cancels bend due be fired before heat dissipates materials do not delaminate to ambient temperature and Cancels residual stress of forma- residual stress. The actuator tion only responds to transient heating of one side or the other. Reverse spring The actuator loads a spring. Better coupling to the ink Fabrication complexity IJ05, IJ11 When the actuator is turned off, High stress in the spring the spring releases. This can reverse the force/distance curve of the actuator to make it compatible with the force/time requirements of the drop ejection. Actuator stack A series of thin actuators are Increased travel Increased fabrication complexity Some piezoelectric ink jets stacked. This can be appropriate Reduced drive voltage Increased possibility of short IJ04 where actuators require high circuits due to pinholes electric field strength, such as electrostatic and piezoelectric actuators. Multiple Multiple smaller actuators are Increases the force available Actuator forces may not add IJ12, IJ13, IJ18, IJ20, IJ22, IJ28, actuators used simultaneously to move the from an actuator linearly, reducing efficiency IJ42, IJ43 ink. Each actuator need provide Multiple actuators can be only a portion of the force positioned to control ink flow required. accurately Linear Spring A linear spring is used to trans- Matches low travel actuator with Requires print head area for the IJ15 form a motion with small travel higher travel requirements spring and high force into a longer Non-contact method of motion travel, lower force motion. transformation Coiled actuator A bend actuator is coiled to Increases travel Generally restricted to planar IJ17, IJ21, IJ34, IJ35 provide greater travel in a Reduces chip area implementations due to extreme reduced chip area. Planar implementations are fabrication difficulty in other relatively easy to fabricate orientations. Flexure bend A bend actuator has a small Simple means of increasing Care must be taken not to IJ10, IJ19, IJ33 actuator region near the fixture point, travel of a bend actuator exceed the elastic limit in the which flexes much more readily flexure area than the remainder of the Stress distribution is very actuator. The actuator flexing uneven is effectively converted from Difficult to accurately model an even coiling to an angular with finite element analysis bend, resulting in greater travel of the actuator tip. Catch The actuator controls a small Very low actuator energy Complex construction IJ10 catch. The catch either enables Very small actuator size Requires external force or disables movement of an ink Unsuitable for pigmented inks pusher that is controlled in a bulk manner. Gears Gears can be used to increase Low force, low travel actuators Moving parts are required IJ13 travel at the expense of duration. can be used Several actuator cycles are Circular gears, rack and pinion, Can be fabricated using standard required ratchets, and other gearing surface MEMS processes More complex drive electronics methods can be used. Complex construction Friction, friction, and wear are possible Buckle plate A buckle plate can be used to Very fast movement achievable Must stay within elastic limits of S. Hirata et al, “An Ink-jet Head change a slow actuator into a the materials for long device life Using Diaphragm Micro- fast motion. It can also convert High stresses involved actuator”, Proc. IEEE MEMS, a high force, low travel actuator Generally high power require- Feb. 1996, pp 418-423. into a high travel, medium force ment IJ18, IJ27 motion. Tapered mag- A tapered magnetic pole can Linearizes the magnetic force/ Complex construction IJ14 netic pole increase travel at the expense of distance curve force. Lever A lever and fulcrum is used to Matches low travel actuator with High stress around the fulcrum IJ32, IJ36, IJ37 transform a motion with small higher travel requirements travel and high force into a Fulcrum area has no linear motion with longer travel and movement, and can be used for lower force. The lever can also a fluid seal reverse the direction of travel. Rotary impeller The actuator is connected to a High mechanical advantage Complex construction IJ28 rotary impeller. A small angular The ratio of force to travel of Unsuitable for pigmented inks deflection of the actuator results the actuator can be matched to in a rotation of the impeller the nozzle requirements by vary- vanes, which push the ink ing the number of impeller vanes against stationary vanes and out of the nozzle. Acoustic lens A refractive or diffractive (e.g. No moving parts Large area required 1993 Hadimioglu et al, EUP zone plate) acoustic lines is used Only relevant for acoustic ink 550,192 to concentrate sound waves. jets 1993 Elrod et al, EUP 572,220 Sharp con- A sharp point is used to concen- Simple construction Difficult to fabricate using Tone-jet ductive point trate an electrostatic field. standard VLSI processes for a surface ejecting ink-jet Only relevant for electrostatic ink jets ACTUATOR MOTION Volume The volume of the actuator Simple construction in the case High energy is typically required Hewlett-Packard Thermal Ink expansion changes, pushing the ink in all of thermal ink jet to achieve volume expansion. jet directions. This leads to thermal stress, Canon Bubblejet cavitation, and kogation in thermal ink jet implementations Linear, normal The actuator moves in a direc- Efficient coupling to ink drops High fabrication complexity may IJ01, IJ02, IJ04, IJ07, IJ11, IJ14 to chip surface tion normal to the print head ejected normal to the surface be required to achieve perpen- surface. The nozzle is typically dicular motion in the line of movement. Parallel to chip The actuator moves parallel to Suitable for planar fabrication Fabrication complexity IJ12, IJ13, IJ15, IJ33, IJ34, IJ35, surface the print head surface. Drop Friction IJ36 ejection may still be normal to Stiction the surface. Membrane An actuator with a high force The effective area of the Fabrication complexity 1982 Howkins U.S. Pat. No. push but small area is used to push actuator becomes the membrane Actuator size 4,459,601 a stiff membrane that is in area Difficulty of integration in a contact with the ink. VLSI process Rotary The actuator causes the rotation Rotary levers may be used to Device complexity IJ05, IJ08, IJ13, IJ28 of some element, such as a grill increase travel May have friction at a pivot or impeller Small chip area requirements point Bend The actuator bends when A very small change in Requires the actuator to be made 1970 Kyser et al U.S. Pat. No. energized. This may be due to dimensions can be converted to from at least two distinct layers, 3,946,398 differential thermal expansion, a large motion. or to have a thermal difference 1973 Stemme U.S. Pat. No. piezoelectric expansion, across the actuator 3,747,120 magnetostriction, or other form IJ03, IJ09, IJ10, IJ19, IJ23, IJ24, of relative dimensional change. IJ25, IJ29, IJ30, IJ31, IJ33, IJ34, IJ35 Swivel The actuator swivels around a Allows operation where the net Inefficient coupling to the ink IJ06 central pivot. This motion is linear force on the paddle is motion suitable where there are opposite zero forces applied to opposite sides Small chip area requirements of the paddle, e.g. Lorenz force. Straighten The actuator is normally bent, Can be used with shape memory Requires careful balance of IJ26, IJ32 and straightens when energized. alloys where the austenic phase stresses to ensure that the is planar quiescent bend is accurate Double bend The actuator bends in one direc- One actuator can be used to Difficult to make the drops IJ36, IJ37, IJ38 tion when one element is power two nozzles. ejected by both bend directions energized, and bends the other Reduced chip size. identical. way when another element is Not sensitive to ambient temp- A small efficiency loss com- energized. erature pared to equivalent single bend actuators. Shear Energizing the actuator causes a Can increase the effective travel Not readily applicable to other 1985 Fishbeck U.S. Pat. No. shear motion in the actuator of piezoelectric actuators actuator mechanisms 4,584,590 material. Radial con- The actuator squeezes an ink Relatively easy to fabricate High force required 1970 Zoltan U.S. Pat. No. striction reservoir, forcing ink from a single nozzles from glass tubing Inefficient 3,683,212 constricted nozzle. as macroscopic structures Difficult to integrate with VLSI processes Coil/uncoil A coiled actuator uncoils or coils Easy to fabricate as a planar Difficult to fabricate for non- IJ17, IJ21, IJ34, IJ35 more tightly. The motion of the VLSI process planar devices free end of the actuator ejects Small area required, therefore Poor out-of-plane stiffness the ink. low cost Bow The actuator bows (or buckles) Can increase the speed of travel Maximum travel is constrained IJ16, IJ18, IJ27 in the middle when energized. Mechanically rigid High force required Push-Pull Two actuators control a shutter. The structure is pinned at both Not readily suitable for ink jets IJ18 One actuator pulls the shutter, ends, so has a high out-of-plane which directly push the ink and the other pushes it. rigidity Curl inwards A set of actuators curl inwards Good fluid flow to the region Design complexity IJ20, IJ42 to reduce the volume of ink that behind the actuator increases they enclose. efficiency Curl outwards A set of actuators curl outwards, Relatively simple construction Relatively large chip area IJ43 pressurizing ink in a chamber surrounding the actuators, and expelling ink from a nozzle in the chamber. Iris Multiple vanes enclose a volume High efficiency High fabrication complexity IJ22 of ink. These simultaneously Small chip area Not suitable for pigmented inks rotate, reducing the volume between the vanes. Acoustic vibra- The actuator vibrates at a high The actuator can be physically Large area required for efficient 1993 Hadimioglu et al, EUP tion frequency. distant from the ink operation at useful frequencies 550,192 Acoustic coupling and crosstalk 1993 Elrod et al, EUP 572,220 Complex drive circuitry Poor control of drop volume and position None In various ink jet designs the No moving parts Various other tradeoffs are Silverbrook, EP 0771 658 A2 actuator does not move. required to eliminate moving and related patent applications parts Tone-jet NOZZLE REFILL METHOD Surface tension This is the normal way that ink Fabrication simplicity Low speed Thermal ink jet jets are refilled. After the Operational simplicity Surface tension force relatively Piezoelectric ink jet actuator is energized, it small compared to actuator force IJ01-IJ07, IJ10-IJ14, IJ16, IJ20, typically returns rapidly to its Long refill time usually IJ22-IJ45 normal position. This rapid dominates the total repetition return sucks in air through the rate nozzle opening. The ink surface tension at the nozzle then exerts a small force restoring the meniscus to a minimum area. This force refills the nozzle. Shuttered Ink to the nozzle chamber is pro- High speed Requires common ink pressure IJ08, IJ13, IJ15, IJ17, IJ18, IJ19, oscillating ink vided at a pressure that oscillates Low actuator energy, as the oscillator IJ21 pressure at twice the drop ejection fre- actuator need only open or close May not be suitable for pig- quency. When a drop is to be the shutter, instead of ejecting mented inks ejected, the shutter is opened the ink drop for 3 half cycles: drop ejection, actuator return, and refill. The shutter is then closed to prevent the nozzle chamber emptying during the next negative pressure cycle. Refill actuator After the main actuator has High speed, as the nozzle is Requires two independent IJ09 ejected a drop a second (refill) actively refilled actuators per nozzle actuator is energized. The refill actuator pushes ink into the nozzle chamber. The refill actuator returns slowly, to pre- vent its return from emptying the chamber again. Positive ink The ink is held a slight positive High refill rate, therefore a high Surface spill must be prevented Silverbrook, EP 0771 658 A2 pressure pressure. After the ink drop is drop repetition rate is possible Highly hydrophobic print head and related patent applications ejected, the nozzle chamber fills surfaces are required Alternative for: IJ01-IJ07, quickly as surface tension and IJ10-IJ14, IJ16, IJ20, IJ22-IJ45 ink pressure both operate to re- fill the nozzle. METHOD OF RESTRICTING BACK-FLOW THROUGH INLET Long inlet The ink inlet channel to the Design simplicity Restricts refill rate Thermal ink jet channel nozzle chamber is made long Operational simplicity May result in a relatively large Piezoelectric ink jet and relatively narrow, relying on Reduces crosstalk chip area IJ42, IJ43 viscous drag to reduce inlet Only partially effective back-flow. Positive ink The ink is under a positive Drop selection and separation Requires a method (such as a Silverbrook, EP 0771 658 A2 pressure pressure, so that in the quiescent forces can be reduced nozzle rim or effective hydro- and related patent applications state some of the ink drop Fast refill time phobizing, or both) to prevent Possible operation of the follow- already protrudes from the flooding of the ejection surface ing: IJ01-IJ07, IJ09-IJ12, IJ14, nozzle. This reduces the pressure of the print head. IJ16, IJ20, IJ22, IJ23-IJ34, in the nozzle chamber which is IJ36-IJ41, IJ44 required to eject a certain volume of ink. The reduction in chamber pressure results in a reduction in ink pushed out through the inlet. Baffle One or more baffles are placed The refill rate is not as restricted Design complexity HP Thermal Ink Jet in the inlet ink flow. When the as the long inlet method. May increase fabrication Tektronix piezoelectric ink jet actuator is energized, the rapid Reduces crosstalk complexity (e.g. Tektronix hot ink movement creates eddies melt Piezoelectric print heads). which restrict the flow through the inlet. The slower refill pro- cess is unrestricted, and does not result in eddies. Flexible flap In this method recently disclosed Significantly reduces back-flow Not applicable to most in jet Canon restricts inlet by Canon, the expanding for edge-shooter thermal ink jet configurations actuator (bubble) pushes on a devices Increased fabrication complexity flexible flap that restricts the Inelastic deformation of polymer inlet. flap results in creep over extended use Inlet filter A filter is located between the Additional advantage of ink Restricts refill rate IJ04, IJ12, IJ24, IJ27, IJ29, IJ30 ink inlet and the nozzle filtration May result in complex con- chamber. The filter has a multi- Ink filter may be fabricated with struction tude of small holes or slots, no additional process steps restricting ink flow. The filter also removes particles which may block the nozzle. Small inlet The ink inlet channel to the Design simplicity Restricts refill rate IJ02, IJ37, IJ44 compared to nozzle chamber has a substan- May result in a relatively large nozzle tially smaller cross section chip area than that of the nozzle, resulting Only partially effective in easier ink egress out of the nozzle than out of the inlet. Inlet shutter A secondary actuator controls Increases speed of the ink-jet Requires separate refill actuator IJ09 the position of a shutter, print head operation and drive circuit closing off the ink inlet when the main actuator is energized. The inlet is The method avoids the problem Back-flow problem is eliminated Requires careful design to IJ01, IJ03, IJ05, IJ06, IJ07, IJ10, located behind of inlet back-flow by arranging minimize the negative pressure IJ11, IJ14, IJ16, IJ22, IJ23, IJ25, the ink-pushing the ink-pushing surface of the behind the paddle IJ28, IJ31, IJ32, IJ33, IJ34, IJ35, surface actuator between the inlet and IJ36, IJ39, IJ40, IJ41 the nozzle. Part of the The actuator and a wall of the Significant reductions in back- Small increase in fabrication IJ07, IJ20, IJ26, IJ38 actuator moves ink chamber are arranged so that flow can be achieved complexity to shut off the motion of the actuator closes Compact designs possible the inlet off the inlet. Nozzle actuator In some configurations of ink Ink back-flow problem is None related to ink back-flow Silverbrook, EP 0771 658 A2 does not result jet, there is no expansion or eliminated on actuation and related patent applications in ink back- movement of an actuator which Valve-jet flow may cause ink back-flow Tone-jet through the inlet. NOZZLE CLEARING METHOD Normal nozzle All of the nozzles are fired No added complexity on the May not be sufficient to displace Most ink jet systems firing periodically, before the ink has a print head dried ink IJ01, IJ02, IJ03, IJ04, IJ05, IJ06, chance to dry. When not in use IJ07, IJ09, IJ10, IJ11, IJ12, IJ14, the nozzles are sealed (capped) IJ16, IJ20, IJ22, IJ23, IJ24, IJ25, against air. The nozzle firing is IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, usually performed during a IJ32, IJ33, IJ34, IJ36, IJ37, IJ38, special clearing cycle, after IJ39, IJ40, IJ41, IJ42, IJ43, IJ44, first moving the print head to a IJ45 cleaning station. Extra power In systems which heat the ink, Can be highly effective if the Requires higher drive voltage Silverbrook, EP 0771 658 A2 to ink heater but do not boil it under normal heater is adjacent to the nozzle for clearing and related patent applications situations, nozzle clearing can May require larger drive trans- be achieved by over-powering istors the heater and boiling ink at the nozzle. Rapid success- The actuator is fired in rapid Does not require extra drive Effectiveness depends substan- May be used with: IJ01, IJ02, ion of actuator succession. In some configura- circuits on the print head tially upon the configuration IJ03, IJ04, IJ05, IJ06, IJ07, IJ09, pulses tions, this may cause heat build- Can be readily controlled and of the ink jet nozzle IJ10, IJ11, IJ14, IJ16, IJ20, IJ22, up at the nozzle which boils the initiated by digital logic IJ23, IJ24, IJ25, IJ27, IJ28, IJ29, ink, clearing the nozzle. In IJ30, IJ31, IJ32, IJ33, IJ34, IJ36, other situations, it may cause IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, sufficient vibrations to dislodge IJ43, IJ44, IJ45 clogged nozzles. Extra power Where an actuator is not nor- A simple solution where applic- Not suitable where there is a May be used with: IJ03, IJ09, to ink pushing mally driven to the limit of its able hard limit to actuator movement IJ16, IJ20, IJ23, IJ24, IJ25, IJ27, actuator motion, nozzle clearing may be IJ29, IJ30, IJ31, IJ32, IJ39, IJ40, assisted by providing an enhanc- IJ41, IJ42, IJ43, IJ44, IJ45 ed drive signal to the actuator. Acoustic An ultrasonic wave is applied to A high nozzle clearing capability High implementation cost if IJ08, IJ13, IJ15, IJ17, IJ18, IJ19, resonance the ink chamber. This wave is of can be achieved system does not already include IJ21 an appropriate amplitude and May be implemented at very low an acoustic actuator frequency to cause sufficient cost in systems which already force at the nozzle to clear include acoustic actuators blockages. This is easiest to achieve if the ultrasonic wave is at a resonant frequency of the ink cavity. Nozzle clearing A microfabricated plate is Can clear severely clogged Accurate mechanical alignment Silverbrook, EP 0771 658 A2 plate pushed against the nozzles. The nozzles is required and related patent applications plate has a post for every Moving parts are required nozzle. A post moves through There is risk of damage to the each nozzle, displacing dried nozzles ink. Accurate fabrication is required Ink pressure The pressure of the ink is temp- May be effective where other Requires pressure pump or other May be used with all IJ series pulse orarily increased so that ink methods cannot be used pressure actuator ink jets streams from all of the nozzles. Expensive This may be used in conjunction Wasteful of ink with actuator energizing. Print head A flexible ‘blade’ is wiped Effective for planar print head Difficult to use if print head Many ink jet systems wiper across the print head surface. surfaces surface is non-planar or very The blade is usually fabricated Low cost fragile from a flexible polymer, e.g. Requires mechanical parts rubber or synthetic elastomer. Blade can wear out in high volume print systems Separate ink A separate heater is provided at Can be effective where other Fabrication complexity Can be used with many IJ series boiling heater the nozzle although the normal nozzle clearing methods cannot ink jets drop e-ection mechanism does be used not require it. The heaters do Can be implemented at no not require individual drive additional cost in some ink jet circuits, as many nozzles can be configurations cleared simultaneously, and no imaging is required. NOZZLE PLATE CONSTRUCTION Electroformed A nozzle plate is separately Fabrication simplicity High temperatures and pressures Hewlett Packard Thermal Ink nickel fabricated from electroformed are required to bond nozzle plate jet nickel, and bonded to the print Minimum thickness constraints head chip. Differential thermal expansion Laser ablated Individual nozzle holes are No masks required Each hole must be individually Canon Bubblejet or drilled ablated by an intense UV laser Can be quite fast formed 1988 Sercel et al., SPIE, Vol. polymer in a nozzle plate, which is typi- Some control over nozzle profile Special equipment required 998 Excimer Beam Applica- cally a polymer such as a poly- is possible Slow where there are many tions, pp. 76-83 imide or polysulphone Equipment required is relatively thousands of nozzles per print 1993 Watanabe et al., U.S. Pat. low cost head No. 5,208,604 May produce thin burrs at exit holes Silicon micro- A separate nozzle plate is micro- High accuracy is attainable Two part construction K. Bean, IEEE Transactions on machined machined from single crystal High cost Electron Devices, Vol. ED-25, silicon, and bonded to the print Requires precision alignment No. 10, 1978, pp 1185-1195 head wafer. Nozzles may be clogged by Xerox 1990 Hawkins et al., U.S. adhesive Pat. No. 4,899,181 Glass Fine glass capillaries are drawn No expensive equipment Very small nozzle sizes are 1970 Zoltan U.S. Pat. No. capillaries from glass tubing. This method required difficult to form 3,683,212 has been used for making indiv- Simple to make single nozzles Not suited for mass production idual nozzles, but is difficult to use for bulk manufacturing of print heads with thousands of nozzles. Monolithic, The nozzle plate is deposited as High accuracy (<1 μm) Requires sacrificial layer under Silverbrook, EP 0771 658 A2 surface micro- a layer using standard VLSI de- Monolithic the nozzle plate to form the and related patent applications machined using position techniques. Nozzles are Low cost nozzle chamber IJ01, IJ02, IJ04, IJ11, IJ12, IJ17, VLSI litho- etched in the nozzle plate using Existing processes can be used Surface may be fragile to the IJ18, IJ20, IJ22, IJ24, IJ27, IJ28, graphic pro- VLSI lithography and etching. touch IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, cesses IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Monolithic, The nozzle plate is a buried etch High accuracy (<1 μm) Requires long etch times IJ03, IJ05, IJ06, IJ07, IJ08, IJ09, etched through stop in the wafer. Nozzle Monolithic Requires a support wafer IJ10, IJ13, IJ14, IJ15, IJ16, IJ19, substrate chambers are etched in the front Low cost IJ21, IJ23, IJ25, IJ26 of the wafer, and the wafer is No differential expansion thinned from the back side. Nozzles are then etched in the etch stop layer. No nozzle Various methods have been tried No nozzles to become clogged Difficult to control drop position Ricoh 1995 Sekiya et al U.S. plate to eliminate the nozzles entirely, accurately Pat. No. 5,412,413 to prevent nozzle clogging. Crosstalk problems 1993 Hadimioglu et al EUP These include thermal bubble 550,192 mechanisms and acoustic lens 1993 Elrod et al EUP 572,220 mechanisms Trough Each drop ejector has a trough Reduced manufacturing com- Drop firing direction is sensitive IJ35 through which a paddle moves. plexity to wicking. There is no nozzle plate. Monolithic Nozzle slit The elimination of nozzle holes No nozzles to become clogged Difficult to control drop position 1989 Saito et al U.S. Pat. No. instead of and replacement by a slit accurately 4,799,068 individual encompassing many actuator Crosstalk problems nozzles positions reduces nozzle clogging, but increases cross- talk due to ink surface waves DROP EJECTION DIRECTION Edge (‘edge Ink flow is along the surface of Simple construction Nozzles limited to edge Canon Bubblejet 1979 Endo et shooter’) the chip, and ink drops are No silicon etching required High resolution is difficult al GB patent 2,007,162 ejected from the chip edge. Good heat sinking via substrate Fast color printing requires one Xerox heater-in-pit 1990 Mechanically strong print head per color Hawkins et al U.S. Pat. No. Ease of chip handing 4,899,181 Tone-jet Surface (‘roof Ink flow is along the surface of No bulk silicon etching required Maximum ink flow is severely Hewlett-Packard TIJ 1982 shooter’) the chip, and ink drops are Silicon can make an effective restricted Vaught et al U.S. Pat. No. ejected from the chip surface, heat sink 4,490,728 normal to the plane of the chip. Mechanical strength IJ02, IJ11, IJ12, IJ20, IJ22 Through chip, Ink flow is through the chip, and High ink flow Requires bulk silicon etching Silverbrook, EP 0771 658 A2 forward (‘up ink drops are ejected from the Suitable for pagewidth print and related patent applications shooter’) front surface of the chip. heads IJ04, IJ17, IJ18, IJ24, IJ27-IJ45 High nozzle packing density therefore low manufacturing cost Through chip, Ink flow is through the chip, and High ink flow Requires wafer thinning IJ01, IJ03, IJ05, IJ06, IJ07, IJ08, reverse (‘down ink drops are ejected from the Suitable for pagewidth print Requires special handling during IJ09, IJ10, IJ13, IJ14, IJ15, IJ16, shooter’) rear surface of the chip. heads manufacture IJ19, IJ21, IJ23, IJ25, IJ26 High nozzle packing density therefore low manufacturing cost Through Ink flow is through the actuator, Suitable for piezoelectric print Pagewidth print heads require Epson Stylus actuator which is not fabricated as part of heads several thousand connections to Tektronix hot melt piezoelectric the same substrate as the drive drive circuits ink jets transistors. Cannot be manufactured in standard CMOS fabs Complex assembly required INK TYPE Aqueous, dye Water based ink which typically Environmentally friendly Slow drying Most existing ink jets contains: water, dye, surfactant, No odor Corrosive All IJ series ink jets humectant, and biocide. Modern Bleeds on paper Silverbrook, EP 0771 658 A2 ink dyes have high water- May strikethrough and related patent applications fastness, light fastness Cockles paper Aqueous, Water based ink which typically Environmentally friendly Slow drying IJ02, IJ04, IJ21, IJ26, IJ27, IJ30 pigment contains: water, pigment, sur- No odor Corrosive Silverbrook, EP 0771 658 A2 factant, humectant, and biocide. Reduced bleed Pigment may clog nozzles and related patent applications Pigments have an advantage in Reduced wicking Pigment may clos actuator Piezoelectric ink-jets reduced bleed, wicking and Reduced strikethrough mechanisms Thermal ink jets (with signifi- strikethrough. Cockles paper cant restrictions) Methyl Ethyl MEK is a highly volatile solvent Very fast drying Odorous All IJ series ink jets Ketone (MEK) used for industrial printing on Prints on various substrates such Flammable difficult surfaces such as as metals and plastics aluminum cans. Alcohol Alcohol based inks can be used Fast drying Slight odor All IJ series ink jets (ethanol, where the printer must operate Operates at sub-freezing temp- Flammable 2-butanol, and at temperatures below the freez- eratures others) ing point of water. An example Reduced paper cockle of this is in-camera consumer Low cost photographic printing. Phase change The ink is solid at room temper- No drying time - ink instantly High viscosity Tektronix hot melt piezoelectric (hot melt) ature, and is melted in the print freezes on the print medium Printed ink typically has a ink jets head before jetting. Hot melt Almost any print medium can be ‘waxy’ feel 1989 Nowak U.S. Pat. No. inks are usually wax based, with used Printed pages may ‘block’ 4,820,346 a melting point around 80° C.. No paper cockle occurs Ink temperature may be above All IJ series ink jets After jetting the ink freezes No wicking occurs the curie point of permanent almost instantly upon contacting No bleed occurs magnets the print medium or a transfer No strikethrough occurs Ink heaters consume power roller. Long warm-up time Oil Oil based inks are extensively High solubility medium for High viscosity: this is a sig- All IJ series ink jets used in offset printing. They some dyes nificant limitation for use in have advantages in improved Does not cockle paper ink jets, which usually require a characteristics on paper Does not wick through paper low viscosity. Some short chain (especially no wicking or and multi-branched oils have a cockle). Oil soluble dies and sufficiently low viscosity. pigments are required. Slow drying Microemulsion A microemulsion is a stable, Stops ink bleed Viscosity higher than water All IJ series ink jets self forming emulsion of oil, High dye solubility Cost is slightly higher than water water, and surfactant. The Water, oil, and amphihilic based ink characteristic drop size is less soluble dies can be used High surfactant concentration than 100 nm, and is determined Can stabilize pigment sus- required (around 5%) by the preferred curvature of pensions the surfactant. 

What is claimed is:
 1. An ink supply unit for a printhead, the ink supply unit comprising a molded component which is engageable with a lid, wherein the molded component is shaped to define a plurality of vias for, respectively, cyan, yellow and magenta ink, the component defining a slot in which the printhead is receivable, so that the vias are in fluid communication with through wafer channels defined in the printhead to supply the printhead with ink; wherein the molded component is also shaped to define a plurality of sub-channels for cyan, yellow and magenta ink, respectively, and three main channels, each main channel in fluid communication with the respective sub-channels for cyan, yellow and magenta ink, each main channel being of greater cross-sectional area than each respective sub-channel; wherein each main channel has cross-sectional dimensions of approximately 1 mm×1mm, each sub-channel has cross-sectional dimensions of approximately 20 μm×100 μm and each via has cross-sectional dimensions of approximately 200 μm×50 μm; and wherein the molded component also defines three ink inlets, each ink inlet being in fluid communication with a respective main channel so that cyan, yellow and magenta ink can flow into the molded component.
 2. An ink supply unit as claimed in claim 1, wherein the ink supply unit is plastic injection molded.
 3. An ink supply unit as claimed in claim 1, wherein the ink supply unit is shaped to define a plurality of pit areas between each sub-channel and corresponding vias.
 4. An ink supply unit as claimed in claim 1, wherein the ink supply unit is shaped to define slots which are shaped to permit snap in insertion of rollers.
 5. An ink supply unit for a printhead the ink supply unit comprising a molded component which is engageable with a lid, wherein the molded component is shaped to define a plurality of vias for, respectively, cyan, yellow and magenta ink, the component defining a slot in which the printhead is receivable, so that the vias are in fluid communication with through wafer channels defined in the printhead to supply the printhead with ink; wherein the molded component is also shaped to define a plurality of sub-channels for cyan, yellow and magenta ink, respectively, and three main channels, each main channel in fluid communication with the respective sub-channels for cyan, yellow and magenta ink, each main channel being of greater cross-sectional area than each respective sub-channel; wherein the molded component defines slots which are shaped to permit snap in insertion of rollers; and wherein the molded component also defines three ink inlets, each ink inlet being in fluid communication with a respective main channel so that cyan, yellow and magenta ink can flow into the molded component. 